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New Endpoint for Ablation of Ventricular Tachycardia: Change in QRS Morphology with Pacing at Protected Isthmus as Index of Isthmus Block


  • Rupa Bala, M.D.: Research grant from Biosense Webster, St. Jude Medical, Medtronic; Speakers honoraria from Biosense Webster.

  • Francis E. Marchlinski, M.D.: Biosense Webster: Sponsored research/advisory panel/lecture honorarium; Boston Scientific/Guidant: Sponsored research/lecture honorarium; GE Healthcare: Advisory panel; Medtronic: Sponsored research/lecture honorarium; St. Jude Medical: Sponsored research/lecture honorarium.

  • Sandhya Dhruvakumar, M.D. and Shuaib A. Latif, M.D.: No conflicts of interest or disclosures declared.

Address for correspondence: Rupa Bala, M.D., Assistant Professor of Medicine, 9 Founders Pavilion, Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104, USA. Fax: 215-662-2879; E-mail:


New Endpoint for Ablation of Ventricular Tachycardia. Introduction: Endpoints confirming block in the critical isthmus in sinus rhythm and with pace mapping have not been established.

Methods and Results: A 44-year-old man with a history of Tetralogy of Fallot presented with recurrent ventricular tachycardia (VT). Entrainment mapping was consistent with a macroreentrant circuit rotating in a clockwise fashion under the pulmonic valve. After termination of the VT in a critical isthmus located on the conal free wall, a pace map proximal to the site of successful ablation was consistent with a change in QRS morphology. This change in QRS morphology suggested critical isthmus block and successful ablation, which was confirmed by noninducibility with programmed stimulation.

Conclusion: Evidence of conduction block can be used as an additional endpoint for successful ablation of VT. (J Cardiovasc Electrophysiol, Vol. 21, pp. 320–324, March 2010)

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